Filter unit



FIG. 1 is a Front elevational view of a filter unit showing my new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a perspective view thereof.

The broken lines in the drawing depict portions of the filter unit that form no part of the claimed design. 

CLAIM The ornamental design for a filter unit, as shown and described. 